The present invention relates to the art of electronic packaging and more particularly to a method of packaging a surface acoustical wave device and the resulting structure.
Surface acoustical wave devices (xe2x80x9cSAW devicesxe2x80x9d), also referred to as standing acoustical wave devices, are piezoelectric electronic components which traditionally are used as narrow band frequency filters, e.g., frequency determining elements in high frequency control applications. During use, an acoustical wave is propagated across the active region of the surface of the SAW device. (The active region is also often referred to as the propagating surface.)
As is well known to those skilled in the art, to prevent disruption of the acoustical wave, the package for the SAW device (the SAW package) must not contact the active region of the SAW device, i.e., the SAW device must be packaged so that a contamination free sealed space exists over the active region of the SAW device. The active region must be allowed to flex.
One conventional method used to form a SAW package is to solder a metal lid over the SAW device leaving a hermetically sealed air gap over the active region. However, metal lids are relatively expensive, which increases the cost of the SAW package. Further, the SAW device becomes heated during some processes of soldering the metal lid, which may damage and ultimately destroy the SAW device.
Typically, plastic molding is not used to package SAW devices because the plastic comes in contact with the SAW device thereby not allowing an acoustical wave to occur by the flexing of the active region.
Accordingly, what is needed is a SAW package which can be fabricated at low cost and does not suffer the drawbacks of the plastic molding.
The present invention includes a mounting for a flip chip surface acoustical wave (xe2x80x9cSAWxe2x80x9d) device. In one embodiment, the SAW device includes a first surface having an active region between a first conductive pad and a second conductive pad. The first and second conductive pads are located on the first surface and on opposite ends of the active region. The SAW device is mounted on a substrate. The substrate includes a first surface having conductive contacts thereon. Conductive connections are present between the first and second conductive pads and corresponding contacts on the first surface of the substrate. A first encapsulant contacts and circumscribes a periphery of the SAW device. Importantly, the first encapsulant, the first surface of the SAW device, and the first surface of the substrate define a free space adjacent to the active region.
The present invention also includes a method of mounting a SAW device. In one embodiment, action 1 of the method provides a SAW device having a first surface and a periphery. The first surface includes an active region between a first conductive pad and a second conductive pad. The conductive pads are located on the first surface and on opposite ends of the active region. Action 2 mounts the SAW device on a substrate so that the first surface of the SAW device faces a first surface of the substrate and each of the first and second conductive pads is juxtaposed with a corresponding conductive contact on the first surface of the substrate. Action 3 forms a conductive connection between each of the first and second conductive pads and the corresponding conductive contact on the substrate. Action 4 applies a viscous first encapsulant material onto the first surface of the substrate so as to circumscribe the periphery of the SAW device. The first encapsulant, the first surface of the SAW device, and the first surface of the substrate define a free space. Finally, action 5 hardens the first encapsulant material.
Advantageously, the first encapsulant forms a seal around the SAW device to protect its active region from the environment. A further advantage provided by the first encapsulant is added security that the conductive pads of the SAW device will remain in a connection with the contacts of the substrate even after distortion of the shape of the SAW device.
The present invention is better understood upon consideration of the detailed description below, in conjunction with the accompanying drawings.